1. Technical Field
When regular maintenance is performed on a chain in which a plurality of inner links and a plurality of outer links are alternately connected to each other so as to be wrapped around a sprocket and ends of the chain are coupled to each other via a joint link to carry out product conveyance or power transmission, the following method is performed. The joint link is removed, and the chain is detached from the sprocket; then, a measurement is performed on a length of the chain, and when a difference between an initial length and a length measured after use reaches a reference value, the chain is replaced, thus preventing occurrence of an accident. However, the foregoing method requires a lot of time and effort for detachment/attachment of the chain, and also has a problem that an operation in a facility equipped with the chain must be stopped for a long period of time.
2. Description of Related Art
Therefore, Japanese Unexamined Patent Application Publication No. 10-332342 discloses the following method. A light beam elongated in a longitudinal direction of a chain is applied to peripheral surfaces of two rollers included in a plurality of rollers of the chain, and an image of a region to which the light beam is applied is taken to obtain two arc-shaped images indicative of outline regions of the rollers; then, points of intersection between straight lines, each of which is parallel to the longitudinal direction of the chain and intersects the associated image at two positions, and the images are determined, and center positions of the rollers are calculated by a computer based on the determined intersection points, so that an elongation of the chain is detected based on a distance between the calculated center positions. The use of the foregoing method enables the detection of the chain elongation without detaching the chain.